Several publications are referenced in this application by author name and year of publication in parentheses in order to more fully describe the state of the art to which this invention pertains. The disclosure of each of these publications is incorporated by reference herein.
Pancreatic cancer is the fifth leading cause of death by cancer in the United States. Twenty-four thousand people die each year from this disease. The 5-year survival for pancreatic cancer patients is less than 5% and the incidence of the disease has tripled over the last 40 years. The molecular basis underlying the pathogenesis of pancreatic adenocarcinoma remains unknown. As a result, the disease has an extremely poor prognosis and lacks early diagnostic and therapeutic modalities.
Normal cellular proliferation is finely regulated by the expression of growth-promoting proto-oncogenes and growth-controlling anti-oncogenes. Mutations, rearrangements, deletions, or amplifications that potentiate the activities of proto-oncogenes result in tumor formation. Similar events that inactivate anti-oncogenes or tumor suppressor genes disrupt their role in the cell as negative regulators of cell growth and proliferation.
Gene amplification has been implicated as a common mechanism by which tumor cells acquire a chemotherapy resistant phenotype. Some amplification units arise at the site of the normal gene, but disperse into the cytoplasm as double minutes (DMs). These DMs may become reincorporated and reamplified as homogeneously staining regions (HSRs) or abnormal banding regions (ABRs) at other sites in the genome. DMs and HSRs may be alternate forms of amplified DNA. The DMs are not inherited stably during cell division because of the lack of centromeres. Integration of DMs into a chromosome is thought to result in the formation of HSRs, which represent a more stable, form of the amplified DNA which is maintained as the cell divides. The mechanisms underlying this process are not completely understood, but appear to be based on recombination and unequal distribution of the amplified DNA into daughter cells.
Cytogenetic amplification has been observed in 8 of 63 primary pancreatic adenocarcinomas analyzed for the presence of DMs. The expression of epidermal growth factor, epidermal growth factor receptor, transforming growth factor, erbB-2, erbB-3, and c-met are elevated in pancreatic cancer (Barton et al., 1991; Korc et al., 1992; Lemoine et al., 1992; Prat et al., 1991).
Using restriction landmark genomic scanning (RLGS), Miwa et al (1996) identified a locus at chromosome 19ql3.1-ql3.2 including the AKT2 gene which was amplified in 20% of pancreatic cancer. Over expression of the AKT2 gene was further shown to be associated with the malignant phenotype of a subset of human ductal pancreatic cancers (Cheng et al., 1996).
No well-defined differentiation pathway has been shown in pancreatic adenocarcinomas, and the biology of this tumor type is generally poorly understood. The present inventors have appreciated a need for the isolation of essential components involved in the regulation of differentiation and proliferation of pancreatic tumor cells. Molecular elucidation of these components will provide novel targets for the development of antiproliferative and diagnostic agents for cancer treatment and diagnosis.